Interest in screening capabilities has resulted in significant investment in thermal neutron analysis (TNA) and fast neutron analysis (FNA), which probe the nuclear structure of matter, rather than the electronic structure of matter as x-ray-based devices do. With more specificity, x-ray devices are sensitive only to variations in density, and thus fail to provide effective identification when materials include certain (light) elements. In TNA, gamma particles resulting from thermal neutron capture reactions in materials of interest (hydrogen and nitrogen) are used in connection with identifying certain materials. FNA is a far more powerful technique and measures either the gamma rays from nuclei activated by a neutron beam or the energy of an attenuated neutron beam.
Pulsed fast neutron analysis (PFNA) has been utilized to perform two-dimensional elemental imaging. This technology, however, requires complex optics and employs a time-of-flight (ToF) technique combined with sophisticated high-flux pulsed accelerator technology to determine neutron energies. These pulsed systems tend to be relatively expensive, prohibiting widespread use.